Submitted by: Anonymous

Answer:
In addition to the fact that colder water can hold more carbon dioxide, and can therefore draw more of it out of the air and reduce the atmosphere's CO2 concentration, there is indeed another reason why periods of extensive glaciation exhibit depressed levels of atmospheric CO2.

First of all, with massive volumes of water locked up in glacial ice, sea levels are reduced, exposing great areas of continental shelf to the atmosphere.  Also, with less precipitation, there may be a several-fold increase in arid land area over the globe during an ice age.  There is also evidence that wind speeds over much of the planet are significantly enhanced during glacial periods; and these several factors combine to produce atmospheric dust loads that may be an order of magnitude greater during glacials than they are during interglacials.

Carried with this dust are particles of iron, an element that is essential to phytoplanktonic photosynthesis, but which is currently present in extremely low concentrations in many important areas of the world's oceans.  Hence, with a vastly enhanced supply of iron being delivered to the surfaces of the globe's seas via air currents during peak glacial periods, phytoplanktonic photosynthesis can be greatly stimulated; and it is this iron-induced increase in atmospheric CO2 fixation at the surfaces of the world's oceans that can dramatically reduce atmospheric CO2 concentrations during the intense cold of a glacial maximum.

At least that's the theory.